"It's not just Apophis we're looking at," Schweickart said. "We need a set of general principles to deal
with this issue."
The favored approach to dealing with a potentially deadly space rock is to dispatch a spacecraft that
would use gravity to alter the asteroid's course, said astronaut Ed Lu, a veteran of a long-duration mission aboard the International Space Station.
The so-called Gravity Tractor could maintain a position near the threatening asteroid, exerting a
gentle tug that over time would deflect the asteroid's path enough to miss Earth.
An asteroid the size of Apophis would take about 12 days of gravity-tugging, Lu said.
Mission costs are estimated at $300 million.
Setting off explosives to move the asteroid would litter space with debris, which might become threats
to Earth as well, Lu added.
The astronauts would like to see NASA stage a demonstration mission to test the concept before it
would actually be needed to change an asteroid's orbit.
"You don't want to be in the position where the very first time you try something it's the real thing," Lu
said.
